Pettit moved to Chicago, where he was a sports broadcaster on WGN-TV and WGN Radio for a variety of different teams during the 1960s, including the Chicago Cubs and Chicago White Sox. He usually worked as the sidekick for the main TV announcer, Jack Brickhouse. His baseball broadcasting style could be described as low-key and businesslike, compared with the excitable Brickhouse. He also broadcast the Chicago Bears, when Brickhouse was busy covering the Cubs or White Sox.

Pettit is most fondly remembered by fans of the Chicago Blackhawks of the National Hockey League. His first love in sports was ice hockey, and he shone at coverage of that sport. He was the original choice to broadcast the NHL's national games on CBS in the late '60s, but Jack Brickhouse, who ran WGN-TV's sports operations, would not release him from his contract to do the games, and the assignment went instead to Dan Kelly of the St. Louis Blues. That dispute led to his, and the team's, moving to WMAQ Radio in 1970. During his career, the Hawks had a number of highs and lows. Regardless, Pettit covered the games with enthusiasm and expertise. His signature catchphrase, which was even worked into the Blackhawks official fight song, "Here Come The Hawks," was "There's a shot... AND A GOAL!!!" He retired from the Blackhawks in 1976, after a dispute over the quality of his broadcast partners, and from all broadcasting in 1980 to pursue other business interests. He was presented with the Foster Hewitt Memorial Award by the Hockey Hall of Fame in 1986.